Biological clock study challenged

A report in the July 26 Science disputes the controversial notion that bright light applied to skin can reset a person’s biological clock.

In 1998, a research group reported, also in Science, that shining light on the back of a person’s knees could delay or advance the brain-driven daily rhythm that influences body temperature, wakefulness, and many other physiological features. The discovery was hailed as potentially a new way to treat jet lag and other disruptions of the body’s biological clock (SN: 7/11/98, p. 24:

The study, however, prompted skepticism from many researchers. Some suggested that the test subjects didn’t have their eyes properly shielded from light. Conventional thinking holds that light gathered by the eye is the only way to entrain the body’s internal timepiece.

In the new work, Kenneth P. Wright Jr. and Charles Czeisler of Brigham and Women’s Hospital in Boston tried to duplicate the original study, while taking extra steps to prevent participants from seeing any light. Shining light behind a person’s knees had no effect on his or her biological clock, they found. The “suggestion that photic signals are carried from the back of the knee to the human brain via the circulatory system is not supported by our data,” they conclude.